Human stem and progenitor cells have been shown to engraft in the marrow and spleen of sublethally irradiated NOD/SCID, sCID, Bg Nude/XID, NOD/SCID r chain (NSG) mice and in fetal organs xenografted in NOD/SCID (SCID/Hu) mice [1]. In some studies, optimal engraftment required administration of specific recombinant human growth factors [2]. Nevertheless, the demonstration of multilineage hematopoiesis in NOD/SCID mice transplanted with isolated human CD34+/CD38- stem cells supports the notion that xenogeneic transplantation in immunodeficient mice may serve as a surrogate model for human transplantation. Given the importance of preclinical in vivo models, the purpose of Core E is to provide CCEH members as well as other UW and FHCRC investigators with the resources and expertise needed to execute xenografting studies in immune deficient mice. The majority of studies involve analysis of hematopoietic reconstituting ability or immune function of defined populations of cells from humans, non-human primates, and dogs. Protocols have also been developed for evaluating the teratoma generating potential of ESC and iPSC, as well as the engraftment and regenerative potential of their derived progeny. Specifically Core E provides: 1) age appropriate NOD/SCID mice through an in-house breeding program, 2) expert consultation on experimental design, 3) help with obtaining lACUC approval, and 4) assistance with and/or full responsibility for conditioning and injecting mice, as well as sampling tissues from live and euthanized animals.